The present invention relates to infinitely variable ratio torque transmissions of the type which transmit torque by means of traction surface pairs in rolling friction contact and, more specifically, to structure for urging the traction surfaces into engagement with one another where the urging force is directly proportional to the torque transmitted.
In a commonly assigned U.S. Pat. No. 4,152,946 issued May 8, 1979 to Yves Jean Kemper and also in U.S. Pat. Nos. 4,112,779 and 4,112,780 both issued Sept. 12, 1978, to the inventors, Yves Jean Kemper and Lucien Bigot, there are disclosed various embodiments of a variable speed torque transmission which generically include a first body having a pair of rolling or traction surfaces of revolution about a first axis, a second body having a pair of rolling or traction surfaces of revolution about a second axis intersecting the first axis at a point of axis intersection and a crank-like body rotatable on the first axis and supporting the second body for movement such that the second axis nutates through a biconical path about the first axis and with the central apex of the biconical path coincident with the point of axes intersection. The traction surfaces on one of the first and second bodies are oppositely convergent or cone-like to provide a variable radial distance from the common axis thereof whereas the traction surfaces on the other of the two bodies may be of a relatively constant radius. Also, the pairs of rolling surfaces on the first and second bodies are respectively interior and exterior so as be frictionally engaged at two points of contact disposed oppositely of the first axis, oppositely of the point of axes intersection and in a plane containing both the first and second axes. The speed ratio of the transmission is varied by shifting the points of traction surface contact relative to the point of axes intersection. In certain embodiments, such as those disclosed in U.S. Pat. No. 4,152,946, such variation in speed ratio is achieved by shifting annular rings constituting one of the first and second bodies axially relative to cone-like surfaces on the other of these two bodies in which the apex half-angle of the cone-like surfaces approximates or is equal to a constant angle of axes intersection. In the embodiments of U.S. Pat. Nos. 4,112,779 and 4,112,780, speed ratio variation and corresponding shifting of the points of traction surface contact occur as a result of changing the angle of the second body which carries internal cylindrical traction surfaces, relative to the first body which carries a pair of axially separable cone-like members or elements defining exterior traction surfaces. In the latter case, the cone-like members are axially shiftable on the first axis through a distance or throw of a magnitude capable of accommodating variation in the angle of axes intersection.
Efficient transfer of torque in all transmission embodiments exemplified by the disclosures of the aforementioned patent documents involves the development of mechanically induced normal forces by which the respective traction surfaces are urged forcibly into engagement with each other at the two points of contact. In most of the disclosed embodiments, the one of the first and second bodies carrying the oppositely converging cone-like surfaces is constituted by a central shaft and a pair of conical members movable axially on the shaft toward and away from the point of axes intersection. The normal friction force is then generated by applying an axially and oppositely directed thrust force to the cone-like traction members to displace them along the axis of the shaft into engagement with the traction surfaces on the other of the two bodies. Examples of structures previously used to accomplish the axial thrusting include expansible fluid chambers, helicoidal ramp arrangements, fluid chambers in combination with inclined ramps and helically grooved control collars.
In those transmission embodiments in which speed ratio variation is achieved by changing the angle of axes intersection, the structure used to thrust the oppositely converging cone-like members axially of the shaft on which they are mounted must be capable not only of providing a normal force commensurate with or proportional to torque transmitted, but also must have sufficient extensibility or throw along the axis of the shaft to accommodate changes in the axial position of the cone-like members when the speed ratio of the transmission is varied. In addition, and because of the overall transmission geometry in all embodiments, machining tolerances and component material distortion under the force loading imposed must be accounted for. In this latter respect, the shaft on which the cone-like members are supported is supported at opposite ends by the crank-like body and is loaded from diametrically opposite directions intermediate the bearing supported ends by reaction to the normal force loading at the two points of traction surface engagement.